The annual world market for diagnostic equipment based on immunoassays has increased considerably in the last decades. The main reason for the success of immunoassays is that it is easy to adjust to various chemical analysis problems. By using different types of detection techniques in combination with immunoassays, a number of important chemical substances can be identified and quantified. Depending on the physical measuring principle, different types of detectors are suitable for different types of analysis problems. Since the introduction of immunoassays, many new detectors have been presented.
A number of magnetic technologies have been incorporated into devices for different quantitative measurement purposes. Examples of the technologies are magnetic permeability (μ), relative magnetic permeability (μr) and relative magnetic susceptibility (μr-1).
The temperature dependency of magnetic permeability (μ), relative magnetic permeability (μr) and relative magnetic susceptibility (μr-1) has been taken into account earlier when constructing devices bases on these technologies. In F. Ibraimi et al, Anal Bioanal Chem DOI 10.1007/s00216-013-7032-9, 1-7, 2013, an inductance coil for measurement of magnetic permeability maintained at a constant temperature (30° C.) is described.
U.S. Pat. No. 6,700,389 describes a device and a method wherein the temperature of an inductive coil is determined to adjust the inductance measured.
U.S. Pat. No. 7,910,063 describes a further approach to compensate for the changes in coil temperature. According to this document, a device and a process for measurement of magnetic permeability is described. Samples are placed in a measuring coil measuring the inductance of the sample, which thereafter is compared and compensated with a wellknown reference signal achieved by measurements at the same temperature conditions. This type of device allows measurements of the magnetic permeability for samples, but suffers from the drawback that two coils have to be used in the device.
All the above mentioned techniques further suffer from the drawback that the temperature-dependent drift of electrical components (other than the inductance coil) present in the electrical circuit limits the sensitivity (signal to noise ratio) of the detector.